METABOLISM AND NUTRITION Effects of Supplemental Phytase and Phosphorus on Histological and Other Tibial Bone Characteristics and Performances of Broilers Fed Semi-Purified Diets H. QIAN,* H. P. VEIT,+ E. T. KORNEGAY,+ V. RAVINDRAN,* and D. M. DENBOW* *Department of Animal and Poultry Sciences, and ^Department of Biomedical Sciences and Pathobiology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0306 ABSTRACT Two trials with day-old chicks were conducted to investigate the effects of supplemental phytase (Natuphos®) on histological, mechanical, and chemical properties of tibia, and performances of broilers fed semi-purified diets containing soybean meal as the only organic P source [0.11% nonphytate P (nP)]. Dietary treatments in Trial 1 were: 1) 0.20% nP, 2) Diet 1 + 800 U of phytase/kg of diet, 3) 0.27% nP, 4) Diet 3 + 600 U of phytase, 5) 0.34% nP, 6) Diet 5 + 400 U of phytase. Supplemental phytase and inorganic P increased tibial length (P < 0.01), shear force (P < 0.001), shear stress (P < 0.05), ash content (P < 0.001), and BW gain and feed intake (P < 0.001) during Trial 1. The hypertrophic zone width at the proximal end of the tibia was decreased (P < 0.05), and the tibial width (P < 0.05) of the long axis of the tibia was increased by the phytase and P supplementation. Supplemental phytase enlarged the cartilaginous and proliferative zones of the tibial proximal end (P < 0.05), and an increase in nP levels produced similar effects. Supplementation of phytase

and P also tended to improve the orderliness of development and arrangement of cartilage and bone cells. Dietary treatments in Trial 2 were: 1) 0.27% nP, 2) Diet 1 + 350 U of phytase, 3) Diet 1 + 1,050 U of phytase, 4) 0.45% nP, 5) 0.54% nP, 6) Diet 5 + 1,050 U of phytase. Broilers fed diets containing relatively high levels of nP and phytase supplementation in Trial 2 gave results similar to those observed in Trial 1. Marked improvements (P < 0.05) in the ash content, shear force, shear stress, length of tibia, BW gain, and feed intake, and reduced hypertrophic zone width were achieved for broilers fed the P-deficient diet supplemented with phytase. Also, supplemental phytase tended to increase the width of cartilaginous and proliferative zones, to increase trabecular bone density, and to improve the orderliness of development and mineralization of cartilage and bone cells. In summary, supplementing a lownP diet with inorganic P or phytase resulted in similar beneficial effects on bone development.

(Key words: phytase, phosphorus, tibia, broiler) 1996 Poultry Science 75:618-626

Nelson et al. (1971) reported that the addition of phytase derived from Aspergillus ficuum to broiler diets resulted in a marked improvement of the utilization of phytate P as measured by ash content of bone. Recently, several researchers have shown that dietary supplementation of broiler diets containing various feedstuffs with microbial phytase improved the availability and retention of P and Ca (Swick and Ivey, 1990; Simons et al, 1992; Hoppe and Schwarz, 1993). Several criteria have been used for the estimation of P availability by broilers, but many researchers prefer growth rate and bone ash content because of its simplicity (Sullivan and Douglas, 1990). There are no known reports of the effects of supplemental phytase on the microscopic or histologic bone development of broilers. Therefore, the objective of this research was to investigate the effects of phytase supplementation of soybean meal-based semi-purified diets with low levels of available P fed to broilers on the histologic, mechanical, and chemical traits of the tibia.

INTRODUCTION Less than one-third of the P in feedstuffs of plant origin is biologically available to monogastric animals (NRC, 1988, 1994). Abnormal bone development is one of the most obvious signs of a P deficiency. Phosphorus deprivation leads to rachitic bones, osteoporosis, osteomalacia, and osteodystrophy, which result from the abnormal growth and arrangement of cartilaginous and bone cells that is due to incomplete or irregular ossification or demineralization. At the same time, Pdeprived bones are shorter and have reduced mass and mineral contents (Edwards and Veltmann, 1983; Yoshida, 1986).

Received for publication July 10, 1995. Accepted for publication January 9, 1996.

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EFFECTS OF PHYTASE AND PHOSPHORUS ON TIBIAL HISTOLOGY TABLE 1. Composition and analysis of the basal diets (as-fed basis), Trials 1 and 2 Nonphytate phosphorus Item

0.20%

0.27%

0.34%

0.45%

0.54%

(